The Traverse Board

The origin of the Traverse Board
is unknown to us today, but we do know
that it's use has has been documented
since
the mid-1500s, and it is likely it was
developed as early as the 1500s.

A normal "Watch"
period aboard a ship, the crew's work periods,
were four hours long. They were
typically broken
up into half-hour segments because it
was more convenient to use a half-hour
sandglass. At the end of each half-hour,
a bell was rung to remind you that it
was time to record how fast you were going during
the past half-hour as well as the
direction you were steering. This
information was obtained from the Traverse Board.

The Traverse Board has a diagram of a
compass on it with all 32 points listed.
The points are the directions the ship
could be sailing. On each of these
points there are eight holes drilled,
from the center to the outside edge. You
therefore have eight concentric circles
covering all of the points of a compass.
Each circle represents one half-hour
segment of an eight-hour watch. In the
center of the compass diagram there are
eight pieces of line with a peg attached
to each. After each half-hour, the
ship's boy would place one of the pegs
in a hole representing the direction the
ship had been sailing for the last half
hour. He would do that for each half
hour of the watch and thereby create a
record at half-hour intervals of all the
courses steered during the watch.

At the bottom of the Traverse Board,
there is a second "table." There are
four rows of holes on the left side and
four rows on the right. Each row
represents a half-hour of the watch and
allows a sailor to record the ship's
speed. Each row corresponds to the
concentric circles found around the
compass. The first concentric circle on
the compass is marked for the direction
traveled at the end of the first half
hour. The speed for that first half hour
is marked on the first row in the lower
table, the drilled holes in the row
representing the ship's speed in knots.
The third hole would be three knots, the
fifth hole, five knots, etc. There are
eight pieces of rope with pegs attached
at the bottom of the Traverse Board to
keep track of the speed during each
half-hour.

At the end of the watch the navigator
can tell the direction and speed at each
half hour interval by looking at his
"computer," the Traverse Board. He then
uses the board to come up with a
composite, or single course and distance
traveled for the four-hour watch period.
It was easy to convert speed to distance
for each half hour: four knots for half
an hour is two nautical miles.

Of
course, if the wind doesn't change at
all during the four hours, neither the
course nor the speed might change, but
winds usually do change and thatís why
there was the need to keep track of
them.